A permanent magnet starter motor uses permanent magnets to create the magnetic field inside the motor. Old starter designs use copper wire coils (field coils) for the same job. Permanent magnet starters are lighter, smaller, and more efficient. Most modern cars use this type, often with a gear reduction design called PMGR (Permanent Magnet Gear Reduction).
You shop for a replacement starter. You see terms like "permanent magnet starter motor" and "PMGR starter." You wonder what they mean. You are not alone.
Most new cars use permanent magnet starters. Older cars use a different design with copper coils. The two types do the same job. But they work in different ways.
This guide explains permanent magnet starter motors in simple terms. It also covers PMGR starters and the pros and cons of this design.
A permanent magnet starter motor is an electric motor. It uses permanent magnets to create a magnetic field. This field works with the rotating part (armature) to produce torque. The torque spins the engine to start it.
Older starters use copper wire coils called field coils. These coils need electric current to create a magnetic field. Permanent magnet starters skip the coils. They use solid magnets that always have a magnetic field.
The permanent magnet type is the standard design in most modern passenger cars and light trucks.
Fixed to the inside of the motor housing. They create the magnetic field without power.
The rotating part with copper windings. It spins when current flows through it.
The electromagnetic switch. It pushes the gear forward and sends power to the motor.
The small gear that meshes with the flywheel to crank the engine.
The process is simple. It happens in a few quick steps when you turn the key.
Key Turn
You turn the key. The solenoid gets power.
Gear Engages
The solenoid pushes the gear into the flywheel.
Motor Spins
Current flows to the armature. The magnets make it spin.
The armature spins because current flows through its copper windings. The permanent magnets create a fixed magnetic field around the armature. The two fields push against each other. This push makes the armature rotate. The rotation goes through the drive gear to the flywheel. The flywheel spins the engine. The engine starts. The gear retracts. The starter stops.
The main difference is the source of the magnetic field. Here is a side-by-side comparison.
| Feature | Permanent Magnet | Field Coil |
|---|---|---|
| Magnetic field source | Permanent magnets | Copper wire coils |
| Weight | Lighter | Heavier |
| Size | More compact | Larger bulk |
| Efficiency | Higher | Lower |
| Current draw | Lower | Higher |
| Cold start performance | Better | Good |
| Cost | Higher (magnets) | Lower |
| Common in | Most modern cars | Older cars, heavy trucks |
Field coil starters use electricity to create the magnetic field. This means they draw more current from the battery. Permanent magnet starters already have the field. They only use current for the armature. This saves power and reduces strain on the battery, especially in cold weather.
PMGR stands for Permanent Magnet Gear Reduction. It is a permanent magnet starter with an extra gear set inside.
The gear reduction set sits between the motor and the drive gear. It slows down the motor speed. It increases the torque at the same time. This means a small motor can produce enough torque to start a big engine.
PMGR starters are the most common type in modern passenger cars. They combine the benefits of permanent magnets with the torque boost of gear reduction.
Motor spins fast
High speed, low torque
Gear set reduces speed
Planetary gears
Output spins slower
Low speed, high torque
Car makers want lighter vehicles. They want better fuel economy. They want smaller engine bays. PMGR starters help with all three goals. A PMGR starter can be 30 to 50 percent lighter than an old field coil starter with the same power. It also draws less current, which means smaller batteries and thinner cables can be used.
No heavy copper field coils means less weight. This helps fuel economy and reduces load on the engine mounts.
The compact design fits in tight engine bays. Car makers have more room for other parts.
Less energy is wasted as heat. More battery power goes into actually cranking the engine.
It uses less power from the battery. This is easier on the battery and the charging system.
Lower current draw means more cranking power when the battery is weak in cold weather.
Fewer internal parts means fewer things can go wrong. No field coils to burn out.
Permanent magnet starters are great. But they are not perfect. Here are the main issues to know about.
Permanent magnets lose strength when they get too hot. If you crank the engine for too long, the starter overheats. The magnets can weaken or even demagnetize. Once the magnets lose strength, the starter produces less torque. It may not be able to start the engine.
Not all permanent magnets are the same quality. Good starters use high-grade neodymium or ferrite magnets. Cheap aftermarket starters may use low-quality magnets. These weak magnets can lose strength over time. The starter may fail much sooner than expected.
PMGR starters have extra gears inside. These gears can wear out or break. The planetary gear set is small. It takes a lot of stress every time you start the engine. If the gears fail, the motor spins but the drive gear does not.
Permanent magnet materials cost more than copper coils. Good magnets are expensive. This means permanent magnet starters usually cost more than old field coil types. But the price gap has narrowed in recent years.
Do not crank the engine for more than 10 to 15 seconds at a time. Wait at least 30 seconds between attempts. This gives the starter time to cool down. It protects the magnets from heat damage. It also protects your battery.
Check if your original starter is permanent magnet or field coil. Replace it with the same type. Do not swap types unless the manufacturer says it is okay.
Look for starters that use high-grade magnets. Cheap magnets fail early. Brand-name starters usually use better materials.
If your car came with a PMGR starter, replace it with another PMGR. The mounting and gear count must match exactly.
A good starter should come with at least a 1-year warranty. Longer warranty means the maker trusts the product.
Horizon supplies high-quality permanent magnet and PMGR starter motors for cars, pickups, and commercial vehicles. All units are tested before shipping.
A: For most modern cars, yes. Permanent magnet starters are lighter, smaller, and more efficient. They draw less current. But field coil starters are still used in some heavy-duty applications because they can handle very high torque loads.
A: PMGR means Permanent Magnet Gear Reduction. It is a starter that uses both permanent magnets and a gear reduction set. The magnets save weight and space. The gear set increases torque. This is the most common starter type in modern cars.
A: Yes, it can. Excessive heat is the main cause. If you crank the engine for too long, the starter overheats. The magnets can weaken. Physical damage or very low-quality magnets can also cause loss of magnetism over time.
A: A good quality permanent magnet starter can last 80,000 to 150,000 miles. The exact life depends on usage, quality, and operating conditions. Cars with auto start-stop systems go through starters faster because the starter cycles many times per day.
A: Sometimes yes, but not always. The mounting holes, gear count, and electrical connections must match. Some manufacturers offer conversion kits. But in most cases, you should replace your starter with the same type that came from the factory.
Send us your OEM part number or vehicle details. The Horizon team will help you find the correct permanent magnet or PMGR starter.
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